For several years it has been known that thalidomide is an effective therapy for aphthous ulceration of the mouth in the setting of Behcet's disease. More recently this has also been demonstrated in HIV associated aphthae. The mechanism of action of thalidomide in this setting remains obscure, however. This study is evaluating the effect of this drug in the treatment of oral aphthae associated with Crohn's disease of the intestine. It is hoped that detailed immunological investigations will enable us to gather insight into the mode of action of thalidomide in this setting. We hope to recruit more patients to this pilot study during the coming year.